Approach Procedures
4-3
There are several types of WAAS approaches. The FMS will
automatically select the best available approach based on current
GPS integrity and will indicate the selection as the HDI source.
The pilot must monitor the HDI source throughout the approach
and use charted minimums appropriate to the approach type. If
an approach type is not indicated by the time the final approach
fix (FAF) is reached and the HDI source is given as FMS,
do not
descend
– the conditions required to fly the approach have not
been met and you must fly the missed approach procedure.
WAAS approach types that may be indicated as the HDI source
include:
•
LNAV (Lateral Navigation)
Provides lateral (horizontal) guidance only, with standard
GPS precision of 0.3 NM full-scale deflection. This is
essentially the same as a non-WAAS GPS approach. It is
flown as any other non-precision approach – observing
step down restrictions, descend to MDA, fly at MDA
altitude to the MAP, and execute the missed approach
procedure if appropriate. Since there is no vertical
guidance associated with this type of approach, the VDI
is not displayed.
•
LNAV+V (Lateral Navigation with Vertical Information)
This mode provides the same lateral navigation as LNAV,
but presents an ILS GS-like presentation on the VDI. The
GPS draws a 3-D picture of the approach based on
crossing the FAF at the depicted altitude. Then it follows
a glidepath from the published approach, which is
typically a 3 degree angle to the touchdown zone. This
type of approach remains a non-precision approach and
does not consider any step-down limitations.
For this approach type, manual coupling to the autopilot
is permitted. After “LNAV+V” is annunciated as the HDI
source but prior to FAF, the NAV (or APPR) button on the
autopilot must be pressed. GS will arm or engage
depending on your position relative to the glide slope. Fly
coupled to the MDA, observing any step down restrictions
as needed. If a level off at the MDA is desired, the ALT
button must be pressed on the autopilot.
